Rabble and rabble arm for furnaces



May 10, 192?.

F. A. FAHRENWALD v RABBLE AND RABBLE ARM FOR FURNACES Filed Jan. 16, 1926 2. Sheets-Sheet Frank A. Fabrenwala Attorneys Patented May 10, 1927.

UNITED STATES FRANK A. FAHRENWALD, or cnrcaeo, rumors.

RABBLE AND RABBLE ARM FOB FURNACES.

Application filed January 16, 1926. Serial No. 81,764.

This invention relates to furnaces and has special reference to process furnaces such as are widely used in roasting or processing ore. and minerals, and its objects are the provision of a new, simplified, and improved rabble arm for use in stirring and ad\'anc ing the ore, minerals, or other material undergoing treatment. Many designs of such furnaces have been made but most 'of them include some form of a swinging or rotating arm to which are secured suitable plows. scrapers, or blades which act upon the hot material. Owing to abrasion by the hot material these blades or scrapers deteriorate more rapidly than the arms and are therefore always fastened replaceably, although heretofore owing to the general use of cast iron for this purpose WhlCll is both weak and subject to corrosion at high temperatures the fastenings were massive, difficult to handle and prone to break or stick; whereas it is desirable that these be simple, light and reliable in order to avoid delay in operating the furnace. Such furnaces are generally provided with doors or openings near the rabble arms and it is desirable that the replacement of blades be such as can be performed from the outside of the furnace with the use merely of long tools since this can be done in a few minutes without cooling the furnace or permitting the material toharden therein; while otherwise it may require several days to cool the parts sufficiently to enable a man to enter, not only wasting much time but also frequently resulting in hardening of the material on the hearths so that starting is. difficult, added to the injury always occasioned to such a device by cooling and reheating.

Merely to make from high temperature alloy the same structure which has previously been made from cast iron would exhibit little advantage and .less invention; but I "have invented a new construction which, when made of high temperature alloy exhibits marked economies in weight, complication, and handling. Another advantage of my construction is that it can be made solely by casting, without requiring any machining thereby enabling the use of many alloysnot otherwise available. Other advantages will become apparent as the description proceeds.

.In the drawing accompanying and forniing a part of this application I have shown a preferred embodiment of mv invention although this drawingis intended rather to illustrate the principles of my inventive ideas than to limit me to any details of phi'sical structure. Fig. 1 illustratcspart o a furnace interior embodying my improvements; Fig. 2 is a broken perspective view of part of an arm with scraper; Fig. 3 is a sectional view corresponding to the line 22 of Fig. 1; Figs. 4, 5, 6, and 7, are top plan views of different forms of scrapers; Fig. 8 is a bottom plan view of part of a rabble arm containing my improvements; and Figs.

9, 10, and 11 show side elevations of different forms of scrapers.

The furnace which I have chosen for an illustrative example has an upright cylindrical side wall 1, a plurality of horizontal circular hearths 2, 3, disposed one above the other, and an uprightaxial shaft 4 traversing all said holes. The hearths are formed with central apertures for the passage of the shaft and alternate hearths have these holes enlarged as at 5 for the upward passage the same purpose, the central holes 7 being small so as to obstruct leakage. Radial arms, 8, 8 are carried by said shaft in a position to sweep over each hearth, these arms preferably being made of I-beam section having a vertical web 10, a top flange 11, and a bottom flange 12, this form combining the features of lightness and strength to amarked degree.

The lowermost flange is preferably made hollow as shown in Figs. 2 and 3, this hollow comprising a longitudinal cylindrical bore 13, and having at one side a narrower slot 14 opening through the fiat bottom face 15. Each scraper comprises a blade 16, shoulder 17, neck 18, and head 19. This head is made of elongated shape, rounded in cross section, and small enough to slip readily. into the bore 13 despite irregularities of casting or warping. The neck 18 is sufficiently narrow to pass loosely through the slot 14 and sufiiciently long to prevent binding of' the top 17 against the lower surface of the arm. The blade 16 is preferably made flat but is displaced at an oblique angle to the longitudinal dimension of the head 19 in order to effect a lateral sweeping of the air and may be either righthanded or left-handed as shown in Figs. 4 and 5 respectively or 6 and 7 respectively.

The angle between blade and head may vary has heretofore been done, it is impossible 50 very widely as indicated being seldom less than 30 and often times at least 4:5" or more. The head 19 may be of the same length as the projection of the blade as shown in Figs. 6, 8, and 9, or it may be shorter than such projection as shown in Figs. 5 and or it may be longer than such projection as illustrated in Figs. 7 and 11. In any case the scrapers are preferably so located that the blades of each arm are spaced longitudinally apart as shown in Figs. 1 and 8, but the blades on opposite sides of the furnace are placed at diii'erent distances from the center so that each blade engages and sweeps laterally the ridgeof material which the preceding blade has left behind. In case the heads are equal to or shorter than the blades it is necessary to employ spacing blocks 20. a

The shoulder 1'2" 01"- each scraper is preferably formed at one side of the neck 18 with a longitudinal angular ridge 21 adapted to engage the bottom surface when the blade is canted sideways as in practical operation audit is sometimes desirable to make the neck 18 slightly oblique as regards the plane of the blade 16 as shown by the lines a-a and 5*?) of Fig. 2 so as to bring the blade substantially vertical in operation.

The wall of the furnace is provided above each shelf or hearth with one or more openings 25 closed by suitable doors so as to enable access to the interior and the arms are so located as to swing past these doors at which time the blades and spacers can readily be introduced and withdrawn without the need of entering the furnace. $0 tar as the present invention is concerned the arms may be attached to the shaft at in any convenient or suitable way. The mode here illustrated comprises hinged provisions 26 for supporting the weight and frangible bolt provisions 2'? for producing the drag as set forth in my companion application tiled.

Owing" to the impossibility of cooling this mechanism by currents of air or water as to employ ordinary iron and steel as construction materials but some high temperature alloy must be employed of which numerous examples are available on the market at the present time. As an example of a suitable composition but not with intent to limit myself thereto 1 have used an alloy containing aproximately chromium 17%, silicon 2%, nickel and the balance iron. My invention, however, is independent of the particular composition of materials used. provided only that the same be one which exhibits the necessary strength at the temperatures employed.

Having thus described my invention what I claim is:

1. A rabble arm approximately I-shaped in cross section, the foot of the I being; thicle ened and hollowed out and the bottom face being slotted, and scrapers having clongated heads received in the hollow and neck portions traversing the slot and blades depending from the arm, each blade making an oblique horizontal angle with its head.

2. A rabble arm approximately ll-shaped in cross section the foot of the I being thickened and hollowed out and the bottom itace being slotted, and scrapers having blades depending from said arm and making an oblique horizontal angle therewith, each blade having a shoulder adjacent to the bottom of the arm and a, neck traversing said slot and a head loosely received in said hollow.

3. A rabble arm having a substantially flat, longitudinally slotted lower face, the interior portion of the arm being hollowed out to-produce an enlarged cavity with which said slot communicates, in combination with a plurality of scrapers having necks successively arranged in said slot and heads successively located in the hollow and blades depending from said necks, said blades being oblique to said necks and connected therewith by abrupt shoulders.

In testimony whereof I hereunto affix my signature, l

FRANK A. FAHRENW'ALD. 

